Carbon grain microphone



Oct. 27, 1931. R. VERMEULEN CARBON GRAIN MICROPHONE Filed March 5, 1930 INVENTOR ROELOF VERMEULEN BY 7 7) f ATTORNEY Patented @ct. 27, 1931 UiTED STATES PATENT OFFICE ROELOF VERMEULEN', F EINDHOVEN, NETHERLANDS, ASSIGNOR T0 RADIO CORCPORA- TION OF AMERICA, A CORPORATION OF DELAWARE CARBON GRAIN MICROPHONE Application filed March 5, 1930, Serial No. 433,213, and in the Netherlands May 3, 1929.

The invention relates to microphones provided with electrodes having a layer of carbon granules therebetween.

In many instances the quality of a microphone of this nature deteriorates very quickly due to the fact that the carbon grains move in a definite direction as the result of the force of gravity and accumulate.

To obviate this disadvantage the bottom of a microphone has been divided into compartments and the carbon grains arranged therein in such a manner that carbon grains of different sizes come to different compartments. Such a construction, however, has

not proved to be effective because the carbon grains still move between the diaphragm and the bottom to form heaps which impede the movement of the diaphragm.

In the microphone according to the presl0 ent invention, the carbon grain layer is divided into variousvparts by one or more partitions extending between the diaphragm and the bottom of the microphone.

Said partitions preferably consist of a sup- !5 ple or elastic material such, for example, as

textile fabric, felt or rubber which may be secured to the diaphragm or to the bottom.

If the electrodes of the microphone are constituted by electrically connected metal layers between which the layer of carbon grains extends, the partitions preferably also extend between these layers, for example, in the shape of a metallic partition. I The invention will be more clearly understood by referring to the accompanying drawings which represent, by way of example, an embodiment of the invention.

In the drawings:

cording to the invention.

Figure 2 is a section of a microphone ac- Figure 1 is a'plan View of a microphone acprovided in the cavity 2. A mica diaphragm 5 which closes the cavity 2, is maintained in its position on the block 1 by means of a clamping ring 6. The carbon grain layer is divided into various parts by partitions 7 which extend between the diaphragm and the bottom. They are made of a supple or elastic material, for example, of textile fabric, felt or rubber, and are glued, for example, with the aid of a rubber solution, to the diaphragm 5.

The partitions also extend between the metal layers of the electrodes 3 and 4 in the form of metallic partitions 8. The spaces between the diaphragm 5 and the electrodes 3 and 1 are also sub-divided by the partitions 7 Claims:-

1. A carbon grain microphone comprising a container, a layer of carbon grains in said container, a pair of electrodes in intimate contact with said layer of carbon grains, a diaphragm separate from said electrodes for closing said container, and means extending from said diaphragm to the bottom of said container to divide said layer of carbon grains into a plurality of sections extending between said electrodes, said means consisting of a plurality of partitions of elastic material.

2. A microphone as'described in claim 1 in which said partitions of elastic material are secured to said diaphragm.

ROELOF VERMEULEN. 

